The present invention relates to a motor-driven compressor and more particularly to a motor-driven compressor mounted on a vehicle.
Hybrid vehicle that is powered by both engine and electric motor varies the ratio of engine drive to motor drive in accordance with the running condition of the vehicle. In such a hybrid vehicle, if a compressor that operates a refrigeration cycle of an air conditioner is driven by the engine of the vehicle, the compressor cannot obtain necessary drive force constantly from the engine. In a hybrid vehicle, therefore, a compressor that is driven by electric power from a battery mounted on the vehicle is used. Such a motor-driven compressor is mounted on the body or engine of the vehicle.
The compressor is driven only by the electric motor when the engine is at a stop, such as during an idle stop. When the motor-driven compressor is driven with the engine at a stop, noise is developed due to the operation of the motor-driven compressor. Main cause of the noise development is the resonance due to the vibration of the body or engine caused by the vibration of the motor-driven compressor transmitted via its mounting rather than the sound radiated from the motor-driven compressor. Various mountings for a motor-driven compressor have been proposed to reduce the vibration transmission from the compressor to the body or engine of the vehicle.
Japanese Patent Application Publication No. 64-44815 discloses a structure for mounting a compressor to an engine block or mounting bracket by screws that are inserted through holes formed through the respective mountings of the compressor and screwed into the threaded holes in the engine block. Each of the through-holes in the mounting is larger in diameter than the screw and has therein a cylindrical sleeve through which the screw can be inserted. The through-hole and the cylindrical sleeve have therebetween a rubber vibration isolator inserted by any suitable means such as adhesion or press fitting. The mountings of the compressor are fixed to the engine block by interposing a rubber member between each mounting of the compressor and the engine block and also between the mounting and the head of each screw and then screwing each screw into the threaded hole of the mounting via the rubber member and the through-hole.
If a motor-driven compressor is used as the compressor of the above-referenced publication, it needs to be grounded to the body or engine of the vehicle. However, the motor-driven compressor and the engine block are electrically insulated by the rubber members interposed between the mountings of the motor-driven compressor and the engine block. For the grounding, the motor-driven compressor and the body or engine need to be connected by a grounding cable. Therefore, the compressor of the above-referenced publication requires an extra assembling process for connecting the grounding cable to the motor-driven compressor, thus increasing the manufacturing cost of the compressor.
The present invention is directed to a motor-driven compressor which reduces the cost for grounding the compressor while reducing the noise development.